Browser fingerprinting, explained

Recognition without storage

A cookie is something a site leaves on your device. A fingerprint is something it measures about your device. Delete every cookie you like — the measurements are still there next time.

On its own, no single measurement identifies anyone. Millions of people have your screen size. But combine a dozen of them and the set becomes rare enough to pick you out of a very large crowd.

What gets measured

Tech Mystic demonstrates these live during your reading, so you can watch your own fingerprint form.

• ✦Canvas rendering: the same drawing produces slightly different pixels on different hardware
• ✦Audio processing: a silent tone rendered in software returns device-specific numbers
• ✦Graphics chip name and its capability limits
• ✦Which fonts are installed, which reflects your software history
• ✦Screen size, pixel density, processor cores and memory bucket
• ✦Time zone and your ordered list of languages

The uniqueness trap

Here is the counter-intuitive part. Fingerprinting measures how unusual you are. A browser stuffed with rare extensions, an exotic font set and an unusual window size is more identifiable than a stock browser on a common phone.

That is why serious anti-fingerprinting work does not try to hide the values. It tries to make everyone report the same ones.

What genuinely helps

Choose defences that make you blend in, and resist the urge to install a dozen privacy extensions on top of each other.

• ✦Tor Browser, which standardises what every user reports
• ✦Firefox's resist-fingerprinting mode, or Brave's randomisation
• ✦Safari, which limits font probing and reports reduced system detail
• ✦Avoiding niche browser builds and unusual window sizes